Apparatus for the incorporation of filamentary material in resinous matrix



July 14, 1970 J AMOS ETAL 3,520,027

APPARATUS FOR THE INCORPORATION OF FIL-AMENTARY MATERIAL IN RESINOUSMATRIX Original Filed Jan. 7, 1966. 2 Sheets-Sheet 1 V 41 kfi:3/40

INVENTQRS- James L. rimos Hrneff L. 5170 BY Robe/'7 1. 5/7 o'er HGENT y.1970 J. L. AMOS Em 3,520,027

APPARATUS FOR THE INCORPORATION OF FILAMENTARY MATERIAL IN RESINOUSMATRIX Original Filed. Jan. 7. 1966 2 Sheets-Sheet 2 INVENTORS I r W 1?..5 6 PM a e mee am MM 4? United States Patent 3,520,027 APPARATUS FORTHE INCORPORATION OF FILAMENTARY MATERIAL IN RESINOUS MATRIX James L.Amos and Arnett L. Bird, Midland, and Robert P. Snyder, Saginaw, Mich.,assignors to The Dow Chemical Company, Midland, Mich., a corporation ofDelaware Application Jan. 7, 1966, Ser. No. 532,819, which is acontinuation-in-part of application Ser. No. 342,659, Feb. 5, 1964,which in turn is a continuation-in-part of application Ser. No. 302,504,Aug. 16, 1963. Divided and this application July 11, 1968, Ser. No.744,096 Int. Cl. B29f 1/02 U.S. Cl. 18-30 11 Claims ABSTRACT OF THEDISCLOSURE Glass reinforced thermoplastics are formed by directly addingchopped filaments and particulate thermoplastic resin to heatfabricating apparatus such as an extruder or pre-plasticizing injectionmolding machine under nonstratifying conditions to provide a glassreinforced molded article.

This application is a divisional application of our copendingapplication Ser. No. 532,819, filed Jan. 7, 1966, which in turn is acontinuation-in-part application of our prior application Ser. No.342,659, filed Feb. 5, 1964, now abandoned, which in turn was acontinuation-in-part application of our prior application Ser. No.302,504, filed Aug. 16, 1963, now abandoned.

This invention relates to apparatus for the incorporation of filamentarymaterial into a thermoplastic resinous matrix, and more particularlyrelates to apparatus for fabricating articles containing filamentaryreinforcing embedded in a resinous matrix.

A wide variety of methods and techniques have been utilized in the pastfor incorporating filaments of various types in plastics which may beheat formed. Among these are included the impregnation of a glass matWith a thermoplastic resinous material, subsequent chopping of theimpregnated mat and molding or otherwise heat forming of the resultantproduct. Other techniques which have been used include the technique ofpassing a roving of the filamentary material through a bath containing asolution or a hot melt of the resinous material, subsequently drying orcooling the coated impregnated filament, then chopping it into granulessuitable for heat forming. These techniques are relatively costly andare not well adapted to large scale production without the use ofrelatively bulky and complicated equipment as well as a relatively highlabor cost. An alternate technique which is found to be more economicalcomprises adding a chopped harl, roving or staple fiber or filament to adry blending apparatus together with an appropriate quantity of finelydivided particulate thermoplastic material. This method suffers fromsuch defects as stratification, or concentration; that is, such a blend,on being subjected to vibration or on being moved from place to place,tends to form regions within the container which contain more or less ofthe filamentary reinforcing material.

It is an object of this invention to provide an apparatus forincorporating filamentary reinforcing agent into a thermoplasticresinous matrix.

Another object of this invention is to provide an apparatus for blendingglass fiber reinforcing with thermoplastic resinous particles to providean article having a maximum fiber length therein.

A further object of this invention is to provide a means of closelyregulating the relative quantities of thermoice plastic resinousmaterial and the fiber reinforcing material within a mixture.

' These benefits and other advantages in accordance with the presentinvention are readily achieved by fabricatmg a filament reinforcedresinous object comprising contaming (a) a stream of finely dividedparticulate resinous material which may be formed by the application ofheat and pressure with (b) a stream of a filamentary reinforcmg agent toform a composite stream wherein the filamentary agent and the resinousmaterial are in close contact with each other, the proportion ofreinforcing agent and resinous material being such that on heatplastification the mixture is extrudable, then heat plastifying theparticulate synthetic thermoplastic resinous material and mechanicallymixing it with the filamentary reinforcing agent and heat fabricatingthe combined stream without subjecting it to Stratification conditions.

Further features and advantages of the present invention :will becomemore apparent when the following specification is considered in view ofthe drawing wherein:

FIG. 1 is a schematic representation of the apparatus of the presentinvention.

FIG. 2 depicts an alternate embodiment thereof.

FIG. 3 is a schematic representation of an alternate method of feedingthe heat fabricating apparatus.

FIG. 4 depicts schematically an alternate heat fabricating apparatus forthe practice of the invention.

FIG. 5 depicts an alternate technique for the practice of the invention.

In FIG. 1 there is illustrated a plastic fabrication apparatus inaccordance with the present invention generally designated by thereference numeral 10. The apparatus 10 comprises in cooperativecombination a supply means 12 having a discharge port 13. Disposedwithin the supply means 12 is a quantity of particulate thermoplasticresinous material 15. The material 15 is delivered through the dischargeport 13 in a stream or layer 16 onto the surface of a belt 17. The belt17 is supported and driven by the pulley 19 in the direction indicatedby the arrow. Generally adjacent the resin supply means 12 is positioneda chopper or comminuting device 21. In cooperative combination with thechopping device 21 is a harl or roving supply 22 which delivers a roving22a to a roving feed means 24. The term harl as employed herein refersto an elongated filamentary material adapted to be supplied in the formof rolls, spools, coils, skeins, and bundles, which on chopping tolengths of from about 4 inch to 1 inch, provides individual fibers orfiber bundles of generally parallel fibers. Typical examples of harl areroving, yarns having about one or fewer twists per chopped length,tapes, mats, tows and the like. The roving feed means comprises a pairof driven rolls 25 and 26. The chopper 21 delivers a stream or layer ofchopped filaments or short fibers 27 to the belt 17 upon which there isformed a layer 18 of particulate resinous material 15. The stream offibers 27 forms a second layer 28. The layers 18 and 28 are thin; thatis, the thickness of the layer 18 does not exceed five particlediameters or thicknesses, whereas the layer 28 has a thicknessproportionate to the quantity of resinous material present in the layer18. As the belt 17 moves in the direction of the arrow, the combinedlayer 18 and 28 is discharged into a supply source or receiver 31 of aheat forming apparatus 32 which fabricates the mixture of resin andfilamentary reinforcing material into the shaped article 33.

In FIG. 2 there is illustrated an alternate arrangement of the inventionwherein a trough 37 is provided adjacent the discharge end of the belt17 and the trough directs the stream of thermoplastic resinous materialand chopped filamentary reinforcing material 39 to a compression moldingapparatus 40 comprising a first heated die 41 and a second heated die42. For the sake of clarity, the associated operating mechanisms havebeen omitted.

In FIG. 3 there is illustrated an alternate arrangement of the inventioncomprising a heat fabricating apparatus generally designated by thereference numeral 45 and a feed arrangement generally designated by thereference numeral 46. The feed arrangement 46 comprises a hopper orgranular resin supply 48 having contained therein a granular orparticulate thermoplastic resin 49. The hopper 48 discharges a stream orlayer 51 of the thermoplastic resinous material 49. A chopper orcomminuting device 52 is positioned generally adjacent the hopper 48. Inthe comminuting device 52 is supplied a roving 53'. The roving 53 isdischarged as a stream or layer of chopped filaments 54 from a chute orguide 56. The heat fabricating apparatus 45 is of the variety known as ascrew injection machine and comprises a barrel 55 having heating means55' and 55", the barrel having defined therein a barrel cavity orheating zone 64 and a feed port 57. A hopper 58 is provided adjacent thefeed port 57. Disposed within the cavity 64 is a reciprocating screw 59.A nozzle 61 is disposed adjacent the end of the barrel 55 remote fromthe feed port 57. The nozzle 61 is in com munication with a means toshape under heat pressure or mold 63. In operation of the embodiment ofFIG. 3, the resin stream 51 and the chopped fibers 54 are fed directlyto the hopper 58 and fall into the cavity 64 where the resinous materialis heat plastified and subsequently discharged into the mold 63.

In FIG. 4 there is illustrated an alternate embodiment of the inventiondesignated by the reference numeral 70. The embodiment 70 compriseschopped filament supply means or a chopper or comminuting device 72being supplied with a plurality of rovings '74 which are discharged fromthe chopper as a stream of filaments 76. Generally adjacent the chopper72 is positioned a resin supply 77 which discharges a stream ofparticulate thermoplastic resin 78. A hopper 79 is positioned generallybeneath the chopped filaments 76 and the resin 78. A mixing device 81 isin operative communication with the hopper 79. The mixing device 81comprises a channel or passageway 82 having contained therein a rotatingblending forwarding flight screw 83. A'blend 84 of resin and choppedfilaments is discharged from the end of the blender mixer '81 remotefrom the hopper 79. The blend is discharged into a heat fabricatingdevice 87. The heat fabricating devicev 87 comprises a preplasticizingextrusion section 88 comprising a heated barrel '89 having heatingmeans'89 and 89", the barrel having contained therein a screw 91. Aninjection cylinder 93 is in operative communication with the barrel 89by means of a port 94. An injection piston or ram 95 is disposed withinthe cylinder 93. The injection cylinder 93 discharges into a mold 97. Inthe operation of the apparatus of FIG. 4, a resin and chopped roving isdischarged into a continuous conveying and blending apparatussuch as themixer 81 and is directly discharged into the screw pre-plasticizer 88where it is heat plastified and subsequently extruded into the injectioncylinder 93.

In FIG. there is depicted a schematic representation of an alternateembodiment in accordance with the present invention wherein a resinsupply means 100 is positioned adjacent a resin transport means ortrough 102. A stream or layer 104 of particulate thermoplastic resinousmaterial is discharged into the trough 102 and conveyed to a dischargeend 105 thereof. A comminuting device 106' is positioned generallyadjacent the resin supply 100. A comminuting device or chopper issupplied with a plurality of rovings 107. The rovings 107 are dischargedfrom the comminuting device 106 as a stream of chopped filaments 108. Afilament conveying means or trough 109 is positioned adjacent thechopper 106 and is adapted to receive the chopped filaments 108. Thehopper 109 has a discharge end 110 generally adjacent the discharge end105 of the resin trough 102. A

flowing stream or layer 112 of chopped filaments 108 issues from thetrough 109. A falling stream or layer 114 of thermoplastic resinousmaterial issues from the trough 102. The discharge portions of thetrough 102 and 110 of the trough 109 are so positioned that the streams112 and 114 flow together and intermesh while falling into a hopper 115disposed on a heat fabricating apparatus 116.

In operation of the embodiment of FIG. 5, the resin supply provides apredetermined quantity of resin to the trough 102, whereas apredetermined quantity of chopped filament is provided to the trough109. The falling layers of chopped filament and particulate resin are sopositioned that while falling they intermingle or contact and theresultant combined stream is processed almost immediately by the heatfabricating device.

It is essential and critical to the operation of the embodiments of thepresent invention illustrated in FIGS. 1 and 2 that the thermoplasticresinous material be supplied in the form of layers such as depicted inthe drawing. By utilizing a continuous or intermittent supply of suchlayers, a uniform composition is provided to the heat forming apparatusand stratification or clumping does not occur as in the case of theconventional techniques.

The embodiment of the invention illustrated in FIG. 3 utilizes the samebasic principle of the embodiments of FIGS. 1 and 2 with the exceptionthat the thin layers are formed when the flowing streams engage thescrew. Thus, the thermoplastic resin mixed with the filamentary materialis heat plastified in what can be visualized as thin layers beingwrapped about and forwarded by the screw of the extrusion machine.Preferably in the practice of the invention, the inventory of the mixedfilamentary and particulate resinous material in the hopper of the heatfabricating machine should be maintained at a value sufiiciently lowthat stratification or separation of the two materials does not occur.Thus, in the most beneficial mode of operation, little or no Opportunityis given to the feed material to stratify or gather together in smallballs or clumps. Some material may be retained in the hopper providedthe quantity is insuflicient and the machine vibration is insufiicientto cause objectionable stratification before the material is advancedthrough the extrusion machine.

The embodiment of the invention illustrated in FIG. 4 is particularlyadvantageous in processing locations where the quantity of resin andfilament required by the apparatus is large and the vertical heightavailable for equipment installation is at a minimum. The resin andchopped filament provided to the mixing device 81 are placed in thehopper of the mixing device at a rate equal to or less than the rate oftakeaway of the flight screw. The rate of travel of the materialconveyed by the flight screw is maintained high relative to thestratification rate of the mixture. Thus, the discharge stream 84 ismaintained at a generally constant level and the material removed fromthe hopper of the heat fabricating apparatus generally in accordancewith the requirements of the embodiment of FIG. 3.

The embodiment of FIG. 5 depicts a particularly advantageous feed systemwherein large quantities of materials are being handled. The streams ofparticulate material are discharged from the troughs and the streamsspread as they fall through the air by placing the resin trough and thefiber trough in appropriate relationship, depending upon the particulatematerials utilized. The dispersed or spread out streams will intermingleto provide intimate admixture of the particulate resinous material andthe fibers.

The apparatus of the invention may be employed with any thermoplasticresinous material which is heat formable and benefits from theincorporation of filamentary reinforcing material.

Typical resinous materials which may be utilized include the alkenylaromatic resins typified by polystyrene,

styrene copolymers and blends and graft copolymers of styrene and rubberand the like. The invention is readily practiced utilizing polyvinylchloride; vinylidene chlo ride copolymers such as are generally known asSarans; superpolyamides such as Nylon 66 (a condensation product ofhexamethylene diamine and adipic acid); the polyolefins includingpolyethylene, polypropylene and resinous copolymers thereof, ethylcellulose, cellulose acetate, rubbers, both natural and synthetic,including polybutadiene, polyisoprene, including the chlorinatedderivatives, mixtures thereof and the like. Beneficially, in order toachieve uniform dispersion of the filamentary reinforcing agents withinthe resinous material, it is desirable that the resinous material be ina particulate form. Generally, the resinous material may have an averageparticle size of from a fine powder to granules which are about /8 inchin diameter and /8 inch in length. However, preferably, the particulateresinous material is a material which will pass through a 40 mesh U.S.Sieve size screen. Advantageously, all of such material is retained on a200 mesh U.S. Sieve size screen. Resinous materials more finely dividedthan that which are retained on a 200 mesh screen are oftentimesdifficult to handle, subject to dusting and expensive to prepare.

A wide variety of filamentary reinforcing agents may be utilizedincluding certain thermoplastic materials when utilized with otherresinous materials which have a significantly lower heat formingtemperature than does the reinforcing material. Particularlyadvantageous and beneficial are the thermoplastic resinous compositionsutilizing filamentary glass or fiberglas as a reinforcing medium.

It is essential and critical to the operation of the embodiments of thepresent invention illustrated in FIGS. 1 and 2 that the materials befirst formed in the form of layers in contact with each other andsubsequently added to the supply of the heat forming equipment.Advantageously, such a supply should be maintained at a minimum ofvolume, otherwise a minor degree of stratification may occur due to thevibration of the heat fabricating apparatus. Most advantageously, wherethe discharge of the layers is close to the feed port of the heatfabricating device, the particulate thermoplastic resinous layer shouldbe maintained at a thickness approaching one particle diameter. Byparticle diameter is meant the major dimension exhibited by a particleof the thermoplastic material in a direction normal to a plane uponwhich the particle is resting.

It is essential and critical to the embodiments illustrated in FIGS. 3,4 and 5 that the particulated resinfilament mixture be removed from thehopper at a rate equal to or greater than the rate of supply. Thus, inall of the embodiments of the invention, the resin and choppedfilamentary materials are conveyed to the zone of heat plastification asrapidly as possible once they have been combined.

The apparatus of the present invention is found to be satisfactory whenthe thermoplastic resinous layer has a thickness of from about 2 toabout 5 particle diameters. However, if the thickness in increasedbeyond this figure, oftentimes the uniformity of the resultant productmay be somewhat less than desired. As is readily understood by anyoneskilled in the art, the desired degree of uniformity is a matterprimarily dependent upon the characteristics desired in the resultantproduct. Oftentimes where less than the most uniform degree ofdispersion is satisfactory, a thicker layer may be utilized. As thelayers of material travel greater distances such as by falling throughthe air, the thickness of the layers may be increased without losing theuniformity. Similarly, as the weight or size of the product of the heatfabricating apparatus is increased, thicker layers may be utilized. Ifdesired, almost any number of alternating layers of resin-filament maybe employed for the desired degree of blending.

Although in FIG. 1 there is illustrated a moving belt passing under ahopper and a chopper to form the reinforcing and the resin layer, othertechniques may be readily employed, such as the use of a vibratoryfeeder which may replace the belt. It is particularly advantageous tocontinuously supply the reinforcing material to the apparatus in theform of a roving. The roving is readily handled by conventional textiletechniques until it is discharged from the chopper, at which time it isdropped directly onto the conveying means. Thus, it is unnecessary tohandle and transfer the chopped filamentary reinforcing material for anygreat distance or to handle it in bulk. By enclosing the chopper resinfeed and hopper, considerable savings are found in cleanliness andhealth. Further, a considerable economic advantage occurs from the useof a roving. Such a feeder eliminates bulky handling equipment and thehealth hazards often associated therewith. By varying the feed rates ofeither the resin or the reinforcing agent or even both, a desired ratioof reinforcing material to resinous matrix in the final product isreadily obtained. By utilizing conventional control mechanisms, theratio of reinforcing agent to resinous material may be varied within asingle piece if the operation is an intermittent molding operation, suchas injection molding or the like. This technique may also be employedwith complex moldings where, for example, it may be desirable to have ahigh proportion of reinforcement in the portion of the object beingformed which is prepared from the material initially fed to the mold fora particular purpose, such as surface impact resistance, abrasion or thelike.

In utilizing the apparatus of the present invention, many of thedifficulties frequently encountered in handling filamentary reinforcedthermoplastic materials are overcome. For example, blending ofparticulate thermoplastic resinous materials is such that an excellentdispersion is obtained and the composition of the product is uniform,whereas blends of the filamentary material with the particulate resintend to form filamentary aggregates or clumps wrich are not readilyseparated. This invention also provides a maximum flexibility offormulation which can be varied quickly and easily and permits theaddition of other adhesives, such as fillers, dyes, pigments, lubricantsand sizing agents by means of a third or fourth or even a fifth streamof additaments either to the layer or to the hopper or supply chamber ofthe forming apparatus.

Automation is readily achieved because of the simplicity of the methodemployed by the apparatus of the present invention. It is particularlyversatile in that even B-stage thermosetting resins may be utilized. Bythe B- stage is meant a thermosetting resin which is solid and may beheat fabricated in a manner similar to a thermoplastic resin prior tobecoming fully cross-linked into a thermoset material.

By way of further illustration, a plurality of shaped articles wasprepared by injection molding a blend of a copolymer of 72 parts ofstyrene and 28 parts of acrylonitrile. The polymeric material was ingranular form and passed a 40 mesh U.S. Sieve size screen and wasretained on a 200 mesh US. Sieve size screen. A feed arrangementsubstantially as illustrated in FIG. 1 was employed. A glass rovingcomprising about 16,000 individual filaments having diameters rangingbetween 0.0003 and 0.0004 inch was utilized. An Ankerwerke screwinjection machine having an 8 ounce capacity cylinder was utilized. Thefeed apparatus was operated intermittently to provide adequate materialfor each shot. The overall feed rate for the resinous material was about15 pounds per hour and the glass was fed at an overall rate of about 4.5pounds per hour. The overall cycle time for each operation was about 50seconds. The cylinder temperature was 475 F. and an injection pressureof about 9000 pounds per square inch was used. An H-shaped complex moldcavity was utilized wherein two 6 x 1 inch test bars were prepared aswell as a disc and a rectangle. The molded partsappeared uniform and on.removal of the thermoplastic resinous material, the glass fibers weredetermined to be uniformly distributed throughout.

A Hydraulic Press Manufacturing Company 300 ounce screw pre-plasticizinginjection molding machine was equipped with a feed substantially asillustrated inFIG. 3, the feed adjusted to operate while the screw wasrotating and provide a mixtureof a copolymer of 70* percent by weightstyrene and 30 percent by weight acrylonitrile and quarter inch choppedfilamentary glass roving directly to the feed port. This material wasprovided at a rate of about 12 pounds per minute when the cylinder wasbeing filled. The part being molded weighed /2 pounds for an overallfeed rate of about 330 pounds per hour of a mixture of 70 parts byweight polymer and 30 parts by weight glass. An examination of themolded part indicated that a highly satisfactory uniform dispersion ofthe chopped glass roving in the polymer was obtained.

In a manner similar to the foregoing illustrations, other particulatethermoplastic resinous materials including polystyrene, polypropylene,polyethylene, copolymers of styrene and methyl methacrylate were blendedwith glass fibers and molded into products having a substantiallyuniform distribution of glass fibers within the resinous matrix.Excellent shaped articles are prepared when blends of polymer are usedinstead of a single polymer compound. Mixtures of equal parts ofpolyvinyl chloride and a copolymer of 70 parts by weight styrene and 30parts by weight acrylonitrile and inch glass fibers provide commensuratebeneficial results. Modification of the above procedure by varying theratio of the resinous and glass components resulted in products having apredetermined distribution of the fiber reinforcing agent throughout themolded product. Application of the hereinbefore described technique waseminently successful when applied to extrusion and compression molding.

As is apparent from the foregoing specification, the present inventionis susceptible of being embodied with various alterations andmodifications which may differ particularly from those that have beendescribed in the preceding specification and description. Forthis-reason it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention.

What is claimed is: v

1. An apparatus for the fabrication of thermoplastic resinous materialshaving filamentary reinforcing, the apparatus comprising in cooperativecombination means to supply particulate thermoplastic resinous material,

means to supply a stream of chopped filaments of desired size,

means to provide predetermined quantities of the particulate materialand filaments simultaneously to a heat fabricating apparatus wherein theheat fabricating apparatus includes means to mechanically admix a heatplastified thermoplastic resinous material with the filaments, and

means to discharge the mixture as a heat plastified thermoplasticstream.

2. The apparatus in accordance with claim 1 wherein the chopped filamentand resinous material fall together directly into the heat fabricatingapparatus by gravity flow.

3. The apparatus of claim 1 wherein the heat fabricating apparatus is ascrew injection machine.

4. The apparatus of claim 1 wherein the heat fabricating apparatus is apiston injection molding machine with a screw plasticizer.

5. Apparatus for the fabrication of thermoplastic resinous materialscomprising in cooperative combination ineans to supply particulatethermoplastic resinous material, the supply means adapted to deliver thethermoplastic resinous material in a relatively thin configuration,

a roving Supply means,

a chopping device adapted to chop the roving into desired lengths, theresin supply and the chopping device so constructed and arranged so asto combine desired quantities of the roving and the thermoplasticresinous material in the form of thin adjacent layers,

a heat fabricating machine, the heat fabricating machine having a supplysource, and

means to deliver the adjacent layers of resin and chopped roving to thesupply source of the heat fabricating machine, wherein the heatfabricating machine has means to mechanically admix the thermoplasticresinous material with the filamentary reinforcing agent while thethermoplastic resinous material is in the heat plastified condition, and

means to shape the resultant heat plastified mixture.

6. The apparatus of claim 5 wherein the heat fabricating machine is aninjection molding machine.

7. The apparatus of claim 5 wherein the heat forming apparatus is acompression molding apparatus.

8. The apparatus of claim 5 wherein the means to convey the layers ofparticulate material and chopped roving comprises a vibratory feeder.

9. The apparatus of claim 5 including means to forward the roving intothe chopping device.

10. The apparatus of claim 1 wherein the means to supply a stream ofchopped filament is a means to supply a roving and means to comminutethe roving to a desired length.

11. An apparatus for the fabrication of thermoplastic resinous materialshaving filamentary reinforcing, the apparatus comprising in cooperativecombination means to supply particulate thermoplastic resinous material,

means to supply a stream of chopped filaments of desired size,

means to provide predetermined quantities of the particulate materialand filaments simultaneously to a heat fabricating apparatus wherein theheat fabricating apparatus is a screw injection machine having a screwand heating means, the screw injection machine thereby heat plastifyingthe resinous material and admixing the heat plastified resinous materialwith the filaments and means to discharge the mixture as a heatplastified thermoplastic stream to a mold adapted to receive the heatplastified stream.

References Cited UNITED STATES PATENTS 3,003,194 10/1961 Hunkeler.3,004,878 10/1961 Tomlinson 264-116 X 3,012,922 12/1961 Wiltshire.3,194,859 7/1965 Wacker 264-122 3,328,383 6/1967 Roscher et al 264122 X3,278,992 10/1966 Strauss 18-30 3,304,282 2/1967 Cadus 264349 3,334,1638/1967 Gilbeit 264122 3,429,003 2/1969 Heider et al. 18-12 3,409,71111/1965 Pashak et al. 264349 FOREIGN PATENTS 161,843 3/1955 Australia.

WILBUR L. MCBAY, Primary Examiner US. Cl. X.R.

